All devices on the Web are recognized by a special number called an IP address, for example 123.123.123.123. If you have a site, the domain name that you enter to open it is for your convenience, but the server where your site files are still has an IP. As there are a lot more websites and devices than there're IP addresses, all shared website hosting servers have a number of websites under the same IP, while when you use a dedicated server you'll get a dedicated IP as well. Even in the first case though, you can get a dedicated IP for your websites and host them on a shared server. An advantage would be that you may get improved search engine rankings as a dedicated IP often means a faster loading website. In addition, you need such an IP if you would like to purchase an SSL certificate for your site and shield the info that your visitors submit on it.